Gas dissolving apparatus and method

ABSTRACT

A method and apparatus for dissolving a gas into a fluid which may contain at least one other dissolved gas. The apparatus includes an inlet tube for receipt of the fluid from a container containing the fluid. A gas inlet is operably connected to the inlet tube for the introduction of gas into the fluid. The mixture of gas and fluid is introduced into a gas transfer device via the inlet tube. The gas transfer device is positioned below the surface of the fluid in the container so that the gas transfer device is hydrostatically pressurized in order to increase the rate and concentration at which the gas is dissolved into the fluid. The gas and fluid mixture is allowed to flow downward through the gas transfer device such that bubbles of gas are dissolved in the fluid. The fluid having the gas dissolved therein enters an outlet means positioned within the gas transfer device. The fluid having the gas dissolved therein flows upward through the outlet means and is released from the gas transfer device while the bubbles of gas which are not dissolved in the fluid are retained in the gas transfer device.

RELATED PATENT APPLICATIONS

[0001] This application is a continuation-in-part of InternationalApplication No. PCTIUS01/30793, filed on Oct. 2, 2001, and assigned tothe same assignee as the present invention. International ApplicationNo. PCT/US01/30793 was published in English, and is a continuation ofU.S. Ser. No. 09/677,369, filed on Oct. 2, 2000, now U.S. Pat. No.6,322,055, and assigned to the same assignee as the present invention.

BACKGROUND OF THE INVENTION

[0002] There are many instances when it is desirable to dissolve a gas,whether soluble or insoluble, into a fluid which may already containother dissolved gases. For example, the macro and microbial organisms inall rivers, lakes, oceans, and all aerobic wastewater treatmentprocesses are based on the presence of sufficient dissolved oxygen tosustain their life processes. Normally, in undisturbed bodies of waterthere is a rather low density of macro and micro organisms in thesurface water and the limited natural absorption of oxygen from the airinto the water is sufficient to maintain sufficient concentrations ofdissolved oxygen in the water to sustain the life processes of that bodyof water. However, with increased population density and industrialactivity, the associated organic water pollution causes a high microbialoxygen demand that natural oxygen aeration processes cannot begin toprovide sufficient oxygen resources. Thus, artificial aerationmechanisms are required to enhance oxygen absorption.

[0003] Some specific examples of oxygenation applications are worthy ofdiscussion. Odors at aerobic wastewater treatment facilities areassociated with the inability to maintain sufficient levels of dissolvedoxygen (“D.O.”). In the absence of sufficient D.O., nitrates are reducedto N₂ gas. In the absence of both D.O. and nitrates, strongly reducingconditions develop and sulfates are reduced to H₂S, also known as“rotten egg gas.” This process can occur in any aquatic system where theoxygen demand exceeds the D.O. supply. In addition, indoles, skatoles,and mercaptans are also generated. These volatile compounds all have anoffensive odor even at very low concentrations.

[0004] The high organic pollution in municipal wastewater of sewer liftstations supports a corresponding high microbial population, which, inturn, requires a high rate of D.O. to meet the demand. If the demand isnot. met, H₂S formation readily occurs, as well as the formation ofother compounds that have an offensive odor. Consequently, sewer forcemains are a common source of odor nuisance for municipal public works.

[0005] Some industries (pharmaceutical, petroleum, and chemical, forexample) create significant air pollution problems in the course ofaerobically treating their wastewater by the use of conventionalaeration systems. The wastewaters contain significant volatileorganics/solvents which are readily biodegradable if they can beretained in the aqueous phase for a sufficient time. The use ofconventional aeration systems has led to the requirement that thewastewater aeration basins must be covered to capture and incinerate theoff gas in order to comply with air emission regulations. The need for acovered basin arises because conventional aeration systems readily stripthe organics/solvents from the aqueous phase, not allowing for asufficient time to biograde in the liquid.

[0006] Aerobic activated sludge processes are dependent upon oxygentransfer and sludge settling and recycle in the secondary clarifiers. Itis now possible to develop high concentrations of sludge concentrationswithin the reactors, such as with the use of aerobic fluidized beds andmoving bed filters, to the point where oxygen transfer becomes thelimiting factor. Specifically, high levels of D.O. are required withoutsubjecting the sludge to high energy dissipation/turbulence conditionswhich could shear off the biofilms or hinder flocculent sedimentation inthe secondary clarifiers.

[0007] Fish farming and shrimp production commonly occurs in largeponds. To maximize production, the ponds are operated at the edge ofD.O. availability. Since a still pond absorbs very little oxygen, thereexists a need for artificial aeration to sustain high levels offish/shellfish production.

[0008] The desire to increase dissolved oxygen levels is also applicableto slow moving rivers (such as the Cuyahoga River flowing throughCleveland, Ohio, and the rivers in Bangkok and Taipei) and canals (suchas the waterways of Chicago, Ill. and the canals of Amsterdam). Manyindustries must curtail production (to considerable economic detriment)due to insufficient D.O. in the rivers, streams, and canals to whichthey discharge their treated wastewaters. Odor and corrosion problemscan also occur in the bottom layer of stratified lakes and reservoirsfeeding hydroelectric power dams. The low D.O. levels also result infish kills.

[0009] Systems for dissolving a gas into a fluid are not limited todissolving oxygen in water. Other gas/fluid combinations include:hydrogenation of vegetable oils, coal liquification, yeast production,Vitamin C production, pharmaceutical and industrial aerobicbioprocesses, and other processes well known in the art.

[0010] Therefore, it is desired to provide an apparatus and method ofdissolving a gas into a fluid possibly containing other dissolved gasesthat has application in at least the following situations:

[0011] Slow moving rivers and canals

[0012] Reservoirs

[0013] Fish, shrimp shellfish, and/or mussel ponds

[0014] Aerobic wastewater treatment systems

[0015] Sewer lift stations

[0016] Wastewater industries such as the pharmaceutical, petroleum, andchemical industries

[0017] Aerated lagoons

[0018] Hydrogenation of vegetable oils

[0019] Coal liquification

[0020] Yeast Production

[0021] Vitamin C product

[0022] Pharmaceutical and industrial aerobic bioprocesses

[0023] Ozonation of water or other fluids

[0024] Dissolving xenon in fluids for injecting into the body

[0025] Supersaturating eye-wash liquids with supersaturated D.O.

[0026] Conventional aeration systems either bubble air through diffusersin the bottom of the aeration tank or splash the water in contact withthe air. These systems typically absorb 1 to 2 lbs. of oxygen perkilowatt hour of energy consumed. Oxygen absorption efficiency isgenerally not an issue with these systems because air is free. Thesesystems are most efficient when the D.O. in the water is near zero andare progressively inefficient as the water D.O. level approachessaturation, i.e., 9.2 ppm at 20° C. at sea level. Because the oxygenused in the aeration process is from the air and therefore at no cost,the costs of such systems emanates from capital costs and operatingcosts. The capital cost of a surface aerator capable of dissolving oneton per day of D.O. is about $40,000. The cost of power for the aeratoris $70 to $140/ton of D.O. If the capital costs are amortized at 8% fora 10 year life, the total cost is approximately $87 to $157/ton of D.O.

[0027] In addition to costs, there are other disadvantages orshortcomings of conventional aeration systems. These shortcomingsinclude: (a) low achievable D.O. concentrations of only 1 to 3 ppm; (b)high off-gas production; (c) high air stripping of volatile organiccontaminants; (d) high energy dissipation in the reactor; (e) flocshear; and (f) limited D.O. supply potential.

[0028] As an alternative to conventional systems using “free” air toincrease D.O. levels, systems now exist which generate or store oxygenon-site and dissolve this generated or stored oxygen into the water.Some of these systems are as economical as conventional aerationsystems. Some of these systems address some of the shortcomings ofconventional aeration systems. However, these systems have their ownshortcomings.

[0029] For example, when high purity oxygen is being transferred intowater, issues arise as to handling of dissolved nitrogen (“D.N.”)already in the water. D.N. is not utilized in an aqueous environment.Air is primarily comprised of 21% oxygen and 79% nitrogen gas. Whenwater is in contact with air for prolonged periods, the water issaturated with D.N. At 20° C., the saturation concentration of D.N. inwater is 16 mg/L. With conventional aeration systems, D.N. levels remainin a steady state. However, when high purity oxygen is introduced intothe water, it results in a reduced D.N. partial pressure which stripsthe D.N. from the dissolved phase into the gas phase where it, in turn,reduces the percentage oxygen composition. The reduction in percentageoxygen composition reduces the partial pressure of oxygen in the gasphase, and the saturation concentration of oxygen, and ultimately therate of oxygen transfer.

[0030] Thus, the presence of D.N. in the incoming water presents atrade-off situation. If high oxygen absorption efficiency is to beachieved, the increased nitrogen gas composition in the gas phase has tobe accepted. This reduces the D.O. concentration which can be achievedin the discharge. Conversely, if high D.O. levels are to be achieved inthe discharge, then the stripped nitrogen in the gas phase has to bewasted to reduce its percentage composition carrying with it acommensurate ratio of oxygen gas and reducing the percentage oxygenabsorption efficiency.

[0031] Therefore, it is desirable to develop an oxygenation system whichmanages the level of D.N. already present in the water, and whichreduces the composition of N₂ of the gas phase to allow for higherpotential D.O. saturation (total gas composition of N₂+O₂=100%).Further, effervescent loss of highly saturated D.O. in the dischargeshould be prevented if the D.N. is reduced. Of course, these principlesare applicable to dissolving a gas into a fluid containing dissolvedgases other than dissolving oxygen in water (containing dissolvednitrogen).

[0032] Another problem associated with prior art systems is the abilityof the systems to provide a protracted period of contact (generallypreferred to be greater than 100 seconds) of the bubbles of oxygen (air)with the water. Prolonged contact of the bubbles with the water helps toensure a high oxygen absorption efficiency. Further, bubbles in thewater should be controlled—the greater number of bubbles of oxygen, thegreater the percentage oxygen absorption efficiency. Therefore, it isdesired to provide an oxygenation system and method which fully utilizesthe bubbles in the system and which prolongs the contact of thosebubbles with the water to increase oxygen absorption efficiency of theapparatus.

[0033] With regard to the systems using oxygen rather than air, it iswell known that high purity oxygen can be transported to the site in theform of liquid oxygen which is subsequently converted to gaseous oxygenfor delivery to the oxygenator apparatus. Alternatively, on-sitegeneration using cryogenic separation or pulsed swing adsorptionproduced O₂ is feasible for oxygen requirements of 0.5 to 40 tons ormore per day. Costs of liquid oxygen transported to the site fluctuatewith the vagarities of site-specific conditions and the number ofregional suppliers in competition, among other factors. Thus, in someinstances, the cost of transported liquid oxygen may be prohibitive.

[0034] In some situations, a very high level of D.O. must be achieved inthe discharge to match the accumulative oxygen consumption demand inorder to prevent anaerobic conditions from developing. Such situationsinclude, but are not limited to those present in primary clarifiers,excessively polluted urban rivers, gravity and force main sewers,combined sewer overflow storage basins, sludge dewatering operations,and wastewater lagoons. As high purity oxygen contains 100% O₂ whereasair contains only 21% O₂, it would be expected that the rate ofoxygenation would be five times as fast, and high purity oxygen would beutilized for such situations. However, as discussed above, intraditional oxygenation systems using high purity oxygen, there is asignificant stripping of N₂ gas already dissolved in the water.Therefore, the full potential of using high purity oxygen instead of airto achieve high levels of D.O. has not been realized.

[0035] The gas transfer reactions in traditional oxygenation systemsusing high purity oxygen have occurred at near ambient pressure. Oxygendissolution into water is enhanced by increased pressure in theoxygen/water contactor (bubble swarm). For example, at 1 atmosphere ofpressure and at 20 degrees Celsius, the dissolved oxygen saturationconcentration is 45 mg/L for water at sea level and in contact with highpurity oxygen. At 2 atmospheres of pressure at the same temperature, thedissolved oxygen concentration saturation increases to 90 mg/L.

[0036] However, the unit energy consumption is excessive if the waterhas to be pumped into the oxygen/water contactor to achievepressurization because there is no practical way to recover this energywhen the water leaves the contactor. However, if the oxygen/watercontactor is placed below the ground surface and pressurized by a statichead of water, the water can be moved into and out of it with negligibleenergy—only frictional losses. Yet, the oxygen transfer is significantlyenhanced without associated energy consumption for pumping to maintainthe pressure.

[0037] For oxygen generated using cryogenic systems, the oxygen can beproduced in either the liquid or gaseous forms. If the oxygen is to beused at the same rate as it is produced, the gaseous state is preferredas it is less expensive to produce the gaseous form. However, if thegenerated oxygen is not used immediately, storage usually requiresgeneration in the liquid state which significantly increases the costsassociated with the generated oxygen, both as to production and due tothe requirement for double-walled liquid oxygen storage tanks.

[0038] Another on-site production system is known as the pulsed swingabsorption (PSA) process which utilizes pressure vessels filled withmolecular sieves. A standard air compressor is used to feed the PSAdevice, and it generates oxygen with a 90% to 95% purity. The outletpressure is related to the pressure of the air compressor which thus isthe major cost factor in operating a PSA system. Therefore, it isdesired to use the lowest possible PSA outlet pressure. In view of theavailable oxygen sources not based on “free” air, it is desirable to usePSA systems.

[0039] Overall, it is desirable to provide an apparatus and method fordissolving a gas into a fluid which: (a) has a low capital cost; (b) hasa low operating cost (kwhr/ton of gas dissolved); (c) discharges highD.O. concentrations; and (d) has a high oxygen absorption efficiency.Ideally, the system should be capable of producing a discharge D.O. ofat least 10 mg/L to 250 mg/L, or more, and have an oxygen absorptionefficiency of at least 80%, all accomplished with reasonable capitalcosts and a low unit operating cost.

SUMMARY OF THE INVENTION

[0040] The present invention is an apparatus and method for dissolving agas (whether soluble or insoluble) into a fluid which may or may notcontain other dissolved gases. For example, the present invention may beused as an oxygenation system, i.e., dissolving oxygen into water (watercontains dissolved nitrogen).

[0041] In one embodiment, the apparatus comprises an inlet, an outlet, abubble contact chamber, an acceleration device, a helix-shaped bubbleharvester, and a bubble return pipe. The inlet receives the fluidcontaining the extraneous dissolved gas and is located at the top of theapparatus. Near the inlet and at the top of the bubble contact chamberis located the acceleration device for acceleration of the fluidtherethrough into the chamber. The acceleration design may comprise ahorizontally oriented plate extending through the entire upper end ofthe chamber and having at least one aperture therein. The chamber ismade of two portions. The upper portion has either a constant or agenerally diverging inside surface. The lower portion is substantiallycylindrical in shape with a closed bottom end having at least oneaperture therethrough. An inlet for introduction of the gas to bedissolved is connected to the chamber. The outlet is operativelyconnected to at least one aperture of the bottom end of the chamber.Residing in the bottom portion of the chamber is a helix-shaped bubbleharvester. The bubble return pipe of the apparatus is verticallyoriented and cylindrical in shape. The bubble return pipe has an openbottom end in the lower portion of the chamber, an open top end in theupper portion of the chamber, and at least one aperture located in thelower portion of the chamber proximate to the harvester.

[0042] During operation of this embodiment, fluid enters the inlet andflows through the acceleration device. The accelerated fluid providesturbulence to prevent the bubble swarm from collapsing and to keep thebubble size small. Without this turbulence, the bubble swarm willcoalesce and collapse, greatly reducing the oxygen absorption rate. Theharvester translates the fluid flow into a horizontal component whichallows the bubbles to rise and attach to the underside of thehelix-shaped harvester. The bubbles then flow upward by gravity andinward due to centrifugal force in the helix. The bubbles either flowinto the bubble return pipe through at least one aperture in the tubeand into the bubble chamber for recycling, or travel upward along theunderside of the helix-shaped harvester until the bubbles rise upwardtoward the bubble swarm. Exiting out the outlet is a fluid containing ahigh concentration of dissolved gas and devoid of bubbles.

[0043] In another embodiment of the apparatus of the present invention,first and second vertical cylindrical tubes are concentrically oriented,with the first tube inside the second tube. The space inside the firsttube is the first inner space and is the space through which fluidcontaining dissolved gas exits upward out of the apparatus. The secondinner space is the space between the first and second tubes and is thespace through which fluid and the dissolved gas enter the apparatus.

[0044] Two alternatives of this invention are disclosed. In onealternative, the combination of an acceleration device, an inlet, ahelix-shaped bubble harvester, and a bubble return tube are placed nearthe bottom of the apparatus. This combination is referred to as the gasdissolver, and operates similarly to the previously describedembodiment. Briefly, fluid flows through the acceleration device in thesecond inner space. The gas is introduced to the second inner spaceimmediately below the acceleration device to result in bubbles and fluidflowing downward within the second inner space. At the harvester,bubbles are returned to the second inner space. The fluid havingdissolved gas exits upward through the first inner space.

[0045] In a second alternative, the combination of an accelerationdevice, a harvester, and a bubble return tube are placed near the top ofthe apparatus. This combination is referred to as the dissolved gasstripper. The apparatus also includes a means for receiving waste gasfrom the oxygen gas absorber in the bottom of the apparatus, including afirst vent located near the gas dissolver, waste gas tube, and a secondvent located above the second harvester. Waste gas (gas from a gasdissolved in the fluid initially but later displaced by the dissolvedgas) exits from the gas dissolved through the first vent and the wastegas tube into the bubble tube of the dissolved gas stripper. At thedissolved gas stripper, waste gas exits the apparatus through the secondvent.

[0046] The dissolved gas stripper function is enhanced by the lowpressure in the bubble swarm at the top of the apparatus, while theoxygen absorber function is enhanced by the increased hydrostatic headat the bottom of the apparatus.

[0047] In yet another embodiment of the apparatus of the presentinvention, the harvester and bubble return pipe are placed near thebottom of the inlet side of a U-tube oxygenator. The use of theharvester and return pipe results in more efficient transfer. Thus, thismodified U-tube oxygenator need not be as deep as a conventional U-tubeoxygenator.

[0048] In another embodiment, the apparatus of the present inventioncomprises a container having fluid therein, an inlet tube, a gas inlet,a gas transfer device, and an outlet tube. The fluid is pumped from thecontainer into the inlet tube. The gas inlet is operably connected tothe inlet tube so that gas is introduced into the fluid. The gastransfer device is positioned below the surface of the fluid in thecontainer so that the gas transfer device is hydrostatically pressurizedin order to increase the rate and concentration at which the gas isdissolved into the fluid. The mixture of fluid and gas is introducedinto the gas transfer device through the inlet tube. This mixture flowsdownward through the gas transfer device such that bubbles of gas aredissolved into the fluid. The fluid having the gas dissolved thereinenters an outlet tube positioned within the gas transfer device. Thefluid having the gas dissolved therein flows upward through the outlettube and is released from the gas transfer device, and is returned tothe container from which the fluid was initially introduced into theinlet tube. The bubbles of gas that are not dissolved into the fluid areretained in the gas transfer device.

[0049] The apparatus and method of the present invention is inexpensiveto produce, install, maintain, and operate when compared to many systemsused for oxygenation, for example. The apparatus and method may be usedto dissolve a gas into a fluid which may or may not contain otherdissolved gases. It has application where oxygenation is required, suchas in slow moving rivers and canals, reservoirs, fish/shellfish/musselponds, aerobic wastewater treatment systems, primary clarifiers, sewerlift stations, wastewater industrial applications, lagoons, and more. Itis also not limited to oxygenation of water, but is applicable for othergas dissolving applications.

[0050] The present invention is also highly efficient in absorption ofthe gas into the fluid. When the embodiment including a stripper isused, this efficiency is further increased. The apparatus may be usedfor fluid applications as well as when hydrostatic pressure isavailable, such as at the beginning of sewer force mains, or when a gastransfer device is positioned below the surface of the fluid to beintroduced into the gas transfer device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0051]FIG. 1 shows a side view of one embodiment of the apparatus of thepresent invention in which the outer tube member is translucent toillustrate the components of the apparatus;

[0052]FIG. 2 shows a cross-sectional view of the apparatus of FIG. 1 atline 2-2 of FIG. 1;

[0053]FIG. 3 shows a cross-sectioned view of the apparatus of FIG. 1 atline 3-3 of FIG. 1;

[0054]FIG. 4 shows a cross-sectioned view of the apparatus of FIG. 1 atline 4-4 of FIG. 1;

[0055]FIG. 5 shows a side view of a second embodiment of the apparatusof the present invention wherein the exterior of the apparatus istranslucent to illustrate the components of the apparatus;

[0056]FIG. 6 shows a side view of a third embodiment of the apparatus ofthe present invention wherein the outer tube member is translucent toillustrate the components of the apparatus;

[0057]FIG. 7 shows a side view of a fourth embodiment of the apparatusof the present invention wherein the tube member is translucent toillustrate the components of the apparatus; and

[0058]FIG. 8 shows a side view of a fifth embodiment of the apparatus ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0059] Referring now to FIG. 1, there is shown a side view of oneembodiment of the apparatus of the present invention in which the outertube member is translucent to illustrate the components of theapparatus. In this embodiment, apparatus 10 is used to oxygenate water.Because water contains dissolved nitrogen which is displaced by thedissolved oxygen, apparatus 10 also permits for outgassing (stripping)of nitrogen gas.

[0060] Apparatus 10 includes first tube member 12, second tube member14, third tube member 16, gas feed inlet 18, accelerator plate 20,bubble harvester 22, waste gas vent 24, and waste gas tube 26. Both theupper end 28 and the bottom end 30 of first tube 62 are open. Theinterior of first tube 12 between upper end 28 and bottom end 30 definesfirst inner space 32. First tube member 12 is oriented in asubstantially vertical orientation and is comprised of a materialimpervious to the passage of fluid therethrough. If the fluid compriseswater, for example, first tube 12 may be comprised of plastic or metal.The material of first tube 12 should also be resistant to corrosioncaused by the fluid.

[0061] Apparatus 10 also includes second tube member 14 oriented in asubstantially vertical orientation. Second tube member is of a diametergreater than the diameter of first tube member 12 and is oriented in asubstantial concentric orientation relative to the first tube member 12.Second tube member 14 has open upper end 34 and closed bottom end 36.The space between the outside of first tube member 12 and the inside ofsecond tube member 14 is second inner space 40. Second tube member 14should also be impervious to the flow of the fluid therethrough and itis preferred that it be resistant to corrosion caused by the fluid.Second tube member 14 should also be made of a material impervious tothe flow of any material on the outside of second tube member 14 and ispreferred to be resistant to corrosion caused by such material. Firstand second tube members 12 and 14 may be comprised of a similarmaterial, but this is not required.

[0062] Third tube member 16 has open upper end 42 and open bottom end44, is cylindrical in shape, and also substantially vertically orientedwithin second inner space 40. Bottom end 44 is on the place formed bybottom end 30 of first tube member 12. Upper end 42 is within secondinner space 40 above bubble harvester 22, waste gas vent 24 and wastegas tube 26, and below accelerator plate 20 and inlet 18. Third tubemember 16 also includes at least one aperture or slot 46 proximateharvester 22. Third tube member 16 should be comprised of a materialimpervious to the flow of fluid or the waste gas therethrough. Thus,third tube member 16 may be comprised of the same material as first tubemember 12 and/or second tube member 14, but this is not required.

[0063] In the embodiment of FIG. 1, third tube member 16 is shown to lieagainst first tube member 12 (see also FIGS. 3 and 4). It is requiredthat third tube member reside within second inner space 40, as explainedin greater detail below. It is not required that third tube member 16 bein contact with first tube member 12 as shown; however, as will beexplained hereinafter, it is advantageous to place third tube member 16closer to the central longitudinal axis of first tube member 12 and ofapparatus 10 and, more specifically, close to the central axis ofhelix-shaped harvester 22.

[0064] Returning now to FIG. 1, apparatus 10 also includes inlet 18,serving as an inlet means for introduction of the gas (in thisillustration oxygen) to be dissolved into the fluid housed in secondinner space 40. The gas may be pumped into inlet 18 by means well knownin the art for introduction of the gas into second inner space 40through second tube member 14.

[0065] Apparatus 10 further comprises accelerator plate 20. Acceleratorplate 20 serves as a means to accelerate the flow of fluid therethrough.As shown in FIG. 2, a cross-sectional view along line 2-2 of FIG. 1, inthis embodiment, accelerator plate 20 comprises a donut-shaped platesubstantially extending horizontally and substantially filling secondinner space 40. Accelerator plate 20 also includes at least one aperture48 for the flow of fluid therethrough.

[0066] Accelerator plate 20 is only one alternative that may be used inthe present invention. Again, the primary object of accelerator plate 20is to accelerate the flow of fluid beneath accelerator plate 20 whencompared to the flow of fluid above accelerator plate 20. Thus, theacceleration means used to accomplish this objective must reside withinthe second inner space 40, need not extend across the entire secondinner space 40, and, overall, may be an accelerator of the type wellknown in the art. For example, a suitable acceleration means may be asmall mixer which, like accelerator plate 20, prevents or inhibits thebubbles from coalescing and collapsing.

[0067] As shown in FIG. 1 and in FIG. 3 (a cross-sectional view alongline 3-3 of FIG. 1), apparatus 10 also includes waste gas vent 24 andwaste gas tube 26. Both waste gas vent 24 and waste gas tube 26 arepositioned below upper end 42 of third tube member 16 and above bubbleharvester 22. In this embodiment, waste gas vent 24 simply comprises atrap to trap rising waste gas. Waste gas tube 26 extends through secondtube member 14 below the upper lip of waste gas vent 24 to capture wastegas and allow it to travel through waste gas tube 26.

[0068] Returning to FIG. 1, apparatus 10 further includes bubbleharvester 22. As shown in FIG. 4, a cross-sectional view of line 4-4 ofFIG. 1, harvester 22 is positioned within second inner space 40 andsubstantially extends from the outside of first tube member 12 to theinside of second tube member 14 while accommodating third tube member 16therethrough. Returning to FIG. 1, harvester 22 is helix-shaped andincludes upper end 50 and bottom end 52. Bottom end 52 of harvester 22is positioned above bottom end 36 of second tube member 14 and belowbottom end 30 of first tube member 12. The upper end 50 of harvester 22is below accelerator plate 20, inlet 18, waste gas vent 24, and wastegas tube 26.

[0069] Based on the above description, the operation of the embodimentof FIG. 1 is now described. Fluid (in this example, water) is allowed toflow downward within second inner space 40 toward accelerator plate 20.Gas (in this example, oxygen) is introduced into second inner space 40at inlet 18. Acceleration plate 20 causes an increase in velocity in thefluid and bubbles below accelerator plate 20 when compared to the flowof fluid above accelerator plate 20. The faster flowing fluid is causedby the restriction of cross-sectional area in second inner space 40 andresults in the creation of downward moving jets of fluid. The downwardmoving fluid jets assist in maintaining a dynamic swarm of bubbles ofthe gas within second inner space 40. Without the jets, the bubble swarmwould coalesce and/or collapse, drastically reducing the gas bubblesurface area per unit volume of liquid within second inner space 40.

[0070] The bubbles continue to flow downward toward helix-shaped bubbleharvester 22. Harvester 22 acts similar to a parallel plate separator inthat the fluid flow is converted into a horizontal component, whichresults in the bubbles rising to the underside of harvester 22 above.This process removes bubbles from the fluid flow and causes the bubblesto rise upward in the opposite direction of the fluid flow along theunderside of harvester 22. The centrifugal force impacted byhelix-shaped harvester 22 also forces bubbles toward the center ofsecond inner space 40. Some bubbles may be, during this process, insufficient contact with the fluid to become dissolved in the fluid. Ifbubbles are not so dissolved, they enter slots 46 of third tube member16. These fugitive bubbles of gas are thus collected in the zone ofharvester 22 of apparatus 10 and conveyed by gravity up third tubemember 16 and into the bubble swarm of second inner space 40.

[0071] Because less than all of the bubbles are absorbed into the fluid,bubbles are continually wasted from apparatus 10. Excess bubbles leaveapparatus 10 by being trapped by waste gas vent 24 and exit apparatus 10by waste gas tube 26. The fluid containing dissolved gas exits apparatus10 by flowing upward through first tube member 12.

[0072] It will be appreciated by those of skill in the art that the gasdissolving apparatus of the present invention is comprised of few partsand of no moving parts, other than might be recognized or desired tointroduce gas through inlet 18 and/or fluid through second inner space40 (see FIG. 6, for example). Thus, the apparatus is cost effective,both as to capital costs and costs of operation. The apparatus does notrequire significant maintenance. The apparatus allows large particles tofreely pass through the system. Yet, it is quite capable of resulting inhigh nonsoluble gas absorption efficiency.

[0073] Referring now to FIG. 5, there is shown a side view of a secondembodiment of the apparatus wherein the exterior of the apparatus istranslucent to illustrate the components of the apparatus. In thisembodiment, apparatus 100 includes inlet 102, dissolved gas feed 103,accelerator plate 104, bubble contact chamber 106, bubble harvester 108,bubble return tube member 110, and outlet 112. Inlet 102 serves as ameans for receipt of the fluid with or without a gas therethrough.Dissolved gas feed 103 serves as a means for introduction of the gas tothe fluid housed in chamber 106. Accelerator plate 104, similar toaccelerator plate 20 of FIG. 1, serves to accelerate the flow of fluidsand bubbles in chamber 106 when compared to the fluid flow in inlet 102.

[0074] Bubble chamber 106 is comprised of first portion 114 and secondportion 116. As illustrated, first portion 114 has a diverging interiorsurface. Second portion 116 is substantially cylindrical and includes abottom surface 118 having at least one aperture 120 therethrough.Aperture 120 is operatively connected to outlet 112.

[0075] Within second portion 116 of chamber 106 is harvester 108. Likeharvester 22 of FIG. 1, harvester 108 is helical and, except for theaccommodation of bubble return tube member 110, substantially extendsacross the interior of second portion 116 of chamber 106.

[0076] Bubble return tube member 110 is substantially vertical andproximate to the center axis of chamber 106. Tube member 110, like thirdtube member 16 of FIG. 1, has open upper end 122, open bottom end 124,and at least one aperture 126. Apertures 126 are located proximateharvester 108 and are below the upper end of harvester 108.

[0077] As will be appreciated by those of skill in the art, theembodiment of FIG. 5 will operate in the presence of hydrostaticpressure, such as in a pump discharge. In such a configuration, therealso is no need to accommodate outgassing of initially dissolved gasesdisplaced by the absorption of the gas. Therefore, the embodiment ofFIG. 3 does not contain any special components for handling waste gas.

[0078] Considering the operation of the apparatus of FIG. 5, fluid isintroduced to apparatus via inlet 102 and gas is introduced via gasinlet 103. Increased jet velocity of the fluid is achieved by passage ofthe fluid through accelerator plate 104 in the manner described inassociation with accelerator plate 20 of FIG. 1. The expandedcross-section of first portion 114 of chamber 106 reduces the downwardvelocity of the fluid to less than or equal to that of the buoyantvelocity of the bubbles of gas in the bubble swarm in chamber 106. Thisreduction in fluid velocity allows retention of a very highconcentration of bubbles in the swarm housed in chamber 106. Theconfiguration of chamber 106 therefore enhances gas absorption.Maintenance of prolonged bubble residence times in the bubble swarm ishelpful in this regard.

[0079] As fluid and bubbles reach harvester 108 in second portion 116 ofchamber 106, harvester 108 translates the fluid flow into a horizontalcomponent which permits the bubbles to rise and attach to the undersideof harvester 108, thereby removing them from the fluid flow. The bubblesthen flow upward by gravity and inward due to centrifugal force inhelix-shaped harvester 108. Some bubbles may, during this process, be insufficient contact with the fluid to become dissolved in the fluid. Ifthe bubbles do not become dissolved, the bubbles enter apertures 126 ofbubble return tube member 110 and flow upward out upper end 122 of tubemember 110 into chamber 106. Thus, apparatus 100 returns fugitivebubbles to enhance efficiency by prolonging their residence times. Fluidhaving gas dissolved therein exits chamber 106 through aperture 120 ofbottom surface 118 of chamber 106 into outlet 112.

[0080] It will be appreciated by those of skill in the art that severalmechanisms contribute to the gas absorption efficiency of the apparatusof FIG. 5. The shape of chamber 106 assists in keeping bubbles incontact with the fluid for an extended period of time to enhanceabsorption. To dissolve oxygen in water, for example, it is desired toforce contact of the bubbles with the water for as much as 100 secondsto ensure absorption. Also, the continuation of harvester 108 and bubblereturn tube member 110 recycle fugitive (unabsorbed) bubbles back intochamber 106. This also increases absorption efficiency.

[0081] It will also be appreciated that the exact shapes of chamber 106need not be as illustrated in FIG. 5. For example, various angles andlengths of first portion 114 of chamber are possible. Also, secondportion 116 need not be cylindrical in shape. Also, the chamber could beof unitary conical shape, unitary cylindrical shape, or any other shapereasonably able to promote the flow of fluid and the bubble swarm asdescribed herein.

[0082] Referring now to FIG. 6, there is shown a side view of a thirdembodiment of the apparatus of the present invention wherein the outertube member is translucent to illustrate the components of theapparatus. In this embodiment, apparatus 150, like apparatus 10 of FIG.1, includes first tube member 12, second tube member 14, third tubemember 16, inlet means 18, accelerator plane 20, first helix-shapedbubble harvester 22, first waste gas vent 24, and first waste gas outlet26. This embodiment further includes second accelerator plate 152,second helix-shaped bubble harvester 154, fourth tube member 156, secondwaste gas vent 158, and second waste gas outlet 160. The apparatusfurther includes fifth tube member 162 connecting first gas tube outlet26 to the open bottom end of fourth tube member 156.

[0083] As will become apparent with the description of apparatus 150below, the lower portion of apparatus 150 is primarily responsible forabsorption of the gas, and the upper portion is primarily responsiblefor stripping an initially dissolved gas which is replaced with theabsorbed gas. If used to oxygenate water, the lower portion is theoxygen absorption and the upper portion is the nitrogen stripper.

[0084] In the embodiment of FIG. 6, apparatus 150 is buried in anexcavated shaft, bottom end 36 of second tube member 14 is approximately10 feet or more below the surface of the earth. First tube member 12 isabout 12 inches in diameter and second tube member 14 is about 36 inchesin diameter. These dimensions are illustrative, not a necessity, and notto be limiting in any respect.

[0085] Also nearby is tank 164 having the fluid therein. Tank outletmeans 166 extends into the fluid residing in tank 164 and is operativelyconnected to upper end 34 of second tube member 14. Tank inlet means 168extends into the fluid residing in tank 164 and is operatively connectedto upper end 28 of first tube member 12. To initiate and/or maintainflow of fluid from tank 164 through tank outlet means 166 into apparatus150, pump means 170 is shown.

[0086] Now, turning to the operation of apparatus 150, fluid is pumpedfrom tank 164 through tank outlet means 166 into upper end 34 of secondtube member 14. In one embodiment, the velocity of fluid entering upperend 34 of tube member 14 is approximately 0.5 ft/sec to 2.0 ft/sec. Thefluid passes through second accelerator plate 152. Second acceleratorplate 152 restricts the cross-sectional area for fluid flow and includesapertures (see FIG. 2) to cause the fluid to accelerate into downwardjets. In one embodiment, the downward jets of fluid move atapproximately 6 ft/sec to 12 ft/sec. The increased velocity jetsmaintain a dynamic bubble swarm in the upper portion of apparatus 150.The rise velocity of the bubbles in this upper portion (only about 0.5ft/sec to 1 ft/sec in one embodiment) is low enough so that most of thebubbles accumulate and remain in the dynamic bubble swarm. The gas fedinto the upper portion originates from first waste gas vent throughfirst waste gas tube 26 as described below. As the gas bubblesaccumulate in second inner space 40 in this upper portion of apparatus150, they are crowded downward and are eventually lost as the bubbleswarm is pushed below second waste gas vent 158 to enter second wastegas tube 160.

[0087] At the upper portion of apparatus 150, as fluid flows downwardthrough the bubble swarm the gas (introduced at inlet means 18originally) is dissolved into the fluid and a gas already dissolved inthe fluid is stripped out of the fluid into the gas phase. Fugitivebubbles which get inadvertently dragged out of the bubble swarm must beefficiently captured and returned to the bubble swarm. This isaccomplished with second helix-shaped bubble harvester 154 and fourthtube member 156 in a manner as previously described in association withcomparable components shown in FIGS. 1 and 5.

[0088] Fluid, devoid of fugitive bubbles, continues downward from thebottom of second harvester 154 toward first accelerator plate 20. In oneembodiment, the velocity of the fluid in this area is about 0.5 ft/secto 2.0 ft/sec. The operation of the device is, at this point, asdescribed in association with apparatus 10 of FIG. 1 Because less thanall of the gas is absorbed in the lower portion of apparatus 150, somebubbles are continually wasted from the system through waste gas vent 24into first waste gas tube 26, through fifth tube member 162 into fourthtube member 156. These bubbles are then processed as described above foreventual exit from the system via second waste gas vent 158 and secondwaste gas tube 160. Of course, fluid containing dissolved gas and devoidof bubbles exits the bottom of first harvester 22 and flows upwardthrough first tube member 12, through tank inlet means 168, into tank164.

[0089] It will be appreciated by those of skill in the art that theembodiment of FIG. 6 reduces the extraneous gas (gas initially dissolvedin the fluid) in the system to enhance absorption of the gas. Theextraneous gas is reduced before the gas dissolver. It will also beappreciated that, although shown as installed in an excavation, theapparatus of FIG. 6 need not be so installed. Instead, apparatus 150 maybe placed in a tube or directly into the fluid.

[0090] Referring now to FIG. 7, there is shown a fourth embodiment ofthe present invention wherein U-tube member 190 of the apparatus istranslucent to illustrate the components of the apparatus. U-tube member190 has an inlet side and an outlet side. In this embodiment, apparatus180 comprises a conventional U-tube oxygenator 182, a helical bubbleharvester 184, and a bubble return pipe (tube member) 186. Harvester 184is similar to the bubble harvesters of FIGS. 1, 5, and 6 and bubblereturn pipe 186 is similar to those of FIGS. 1, 5, and 6.

[0091] Fluid enters apparatus 180 on the inlet side of U-tube member190. U-tube oxygenator 182 includes inlet 188 for introduction of thegas (such as oxygen) to be dissolved into the fluid (such as water)housed in U-tube member 190. In one alternative embodiment of thepresent invention, inlet 188 is vertically oriented and extends throughthe inlet side of U-tube member 190. In this embodiment, harvester 184is placed proximate the bottom of the inlet side of the U-tube member190.

[0092] During operation of apparatus 180, harvester 184 and bubblereturn pipe 186 serve the same functionality as described in associationwith the embodiments of FIGS. 1, 5, and 6. Specifically, as bubble movedown the inlet side of the U-tube member 190, undissolved (fugitive)bubbles flow upward against the underside of harvester 184. During thisprocess, some bubbles may be in sufficient contact with the fluid tobecome dissolved in the fluid. If the bubbles are not so dissolved, theythen flow into the apertures of bubble return pipe 186 to be returned tothe bubble swarm above harvester 184. Exiting out the outlet side ofU-shaped tube member 190 is the fluid containing a high concentration ofdissolved gas and devoid of bubbles.

[0093] With regard to the embodiment of FIG. 7, it will be appreciatedby those of skill in the art that use of harvester 184 to capturebubbles results in a more efficient transfer of gas into the fluid. As aresult, the U-tube apparatus does not have to be as deep as aconventional U-tube apparatus to achieve the same absorption levels anddissolved oxygen concentrations.

[0094] It will be appreciated by those of skill in the art that thepresent invention solves several shortcomings of the prior art and canbe used to dissolve soluble and insoluble gases. The apparatus managesthe dissolved gases initially present in the fluid and stripped by thedissolved gas. The apparatus provides a high bubble area per volume offluid to result in a high reduction in dissolved gas deficit. Fugitivebubbles are effectively separated and recycled to increase thepercentage absorption efficiency of the gas. Hydrostatic pressurizationrather than mechanical pressurization is used for dissolving the gas,thereby reducing operational costs. Also, gas is fed into a pressurizedfluid chamber without the necessity of equal pressure from a PSAgenerator or other oxygen source.

[0095] It will also be appreciated that the harvester and bubble returnpipe of the present invention may be used in any container containingfluid, and need not be vertically oriented as illustrated in FIGS. 1, 5,6, and 7. Instead, the harvester/bubble return pipe may be used tocapture bubbles from any fluid flowing in a pipe or conduit (or othercontainer). Further, the harvester/bubble return pipe combination isuseful whether or not any gas is to be dissolved into the fluid.

[0096] It will be further appreciated that the use of theharvester/bubble return pipe combination can reduce the cross-sectionand/or depth of bubble contactor of any apparatus in which it is used.Such reductions result in a lower cost of the apparatus and any cost ofexcavation of the apparatus, if applicable.

[0097] Referring now to FIG. 8, there is shown a side view of a fifthembodiment of the apparatus of the present invention. In thisembodiment, apparatus 200 utilizes high purity oxygen in order toachieve high concentrations of dissolved oxygen in water. However, itwill be appreciated by those of skill in the art that apparatus 200 mayalso be utilized to dissolve other types of gases into other types offluids.

[0098] Apparatus 200 includes container 205, gas feed 210, inlet tube220, gas transfer device 230, and outlet tube 240. Container 205contains water. In the embodiment shown in FIG. 8, container 205comprises a tank. In this embodiment, the tank is impervious to thepassage of water therethrough. The material of the tank is resistant tocorrosion caused by the water. For example, the tank may be comprised ofplastic or metal. It will be recognized by those of skill in the artthat in other embodiments of the present invention container 205 maycomprise a natural container, such as, for example, a lagoon, or asewage pool.

[0099] In the embodiment of the present invention shown in FIG. 8, gastransfer device 230 comprises an upper end 232, and a closed bottom end234. In this embodiment, upper end 232 is closed. However, in otherembodiments of the invention upper end 232 may be open. In theembodiment shown in FIG. 8, gas transfer device 230 further comprises afirst portion 231 and a second portion 233. As illustrated, firstportion 231 has a diverging interior surface. Second portion 233 issubstantially cylindrical. In an alternative embodiment, the gastransfer device simply has a diverging interior surface and is generallyconical in shape. As explained in more detail below, other embodimentsof a gas transfer device may be utilized in apparatus 200.

[0100] Inlet tube 220 and outlet tube 240 may be of any size and shapeprovided that each of inlet tube 220 and outlet tube 240 permit forappropriate transfer of volume of fluid at desired flow rates. Further,inlet tube 220 and outlet tube 240 are comprised of a materialimpervious to the passage of fluid therethrough. It is also desired thatthe material of inlet tube 220 and outlet tube 240 be resistant tocorrosion caused by the fluid. If the fluid comprises water, forexample, inlet tube 220 and outlet tube 240 may be comprised of plasticor metal. Inlet tube 220 and outlet tube 240 may be comprised of asimilar material, but this is not required.

[0101] A first end 221 of inlet tube 220 is positioned within container205, and is adapted for the receipt of the fluid from container 205 towhich the high purity oxygen will be introduced. In the embodiment shownin FIG. 8, the water from container 205 is pumped into first end 221 ofinlet tube 220 via a pump 215 of a type well know in the art. A secondend 222 of inlet tube 220 is adapted for the introduction of the mixtureof the fluid and the high purity oxygen into gas transfer device 230through upper end 232, as discussed below. In the embodiment shown inFIG. 8, second end 222 extends through upper end 232.

[0102] A first open end 241 of outlet tube 240 is positioned within thesecond portion 233 of gas transfer device 230. Outlet tube 240 extendsthrough upper end 232. A second end 242 of outlet tube 240 is positionedoutside of gas transfer device 230, and is adapted for the release ofoxygenated water outside of gas transfer device 230. In the embodimentshown in FIG. 8, second end 242 is positioned within container 205.

[0103] Gas transfer device 230 is positioned below fluid surface 207 inorder to create increased hydrostatic pressure in gas transfer device230. In the embodiment of the present invention shown in FIG. 8, amidpoint of longitudinal axis 236 of gas transfer device 230 ispositioned about 10 feet below fluid surface 207 in order to create theincreased hydrostatic pressure in gas transfer device 230. However, thegas transfer device may be positioned less than 10 feet below fluidsurface 207. In addition, gas transfer device 230 may be positioned asmuch as 100 feet or more below fluid surface 207.

[0104] The only requirement for this fifth embodiment of the presentinvention is that gas transfer device 230 be positioned below fluidsurface 207 in order to create increased hydrostatic pressure in the gastransfer device 230, which in turn increases the concentration ofdissolved oxygen in the oxygenated water released from gas transferdevice 230. In the embodiment of the present invention shown in FIG. 8,gas transfer device 230 is positioned underground in an undergroundstructure 235. In this embodiment, underground structure 235 comprisesan excavated caisson; however, the gas transfer device may be positionedunderground in a variety of different manners. In this embodiment, gastransfer device 230 is positioned underground as fluid surface 207 isbelow ground level.

[0105] Gas transfer device 230 need not be positioned underground.Instead, gas transfer device 230 simply must be positioned below fluidsurface 207. For example, in one embodiment of the present inventioncontainer 205 may be positioned 30 feet above ground level. Thus, inthis embodiment, gas transfer device 230 need not be positionedunderground in order for gas transfer device 230 to be positioned belowfluid surface 207.

[0106] Apparatus 200 further comprises gas feed 210 operably connectedto inlet tube 220 for the introduction of gas (in this illustration highpurity oxygen) into the water contained within inlet tube 220. The gaswill subsequently be dissolved into the water, as explained below. Gasfeed 210 is operably connected to inlet tube 220 between first end 221and second end 222. In an alternative embodiment, gas feed 210 mayintroduce the gas directly into gas transfer device 230. The gas may bepumped into gas feed 210 by means well know in the art. The flow ratesof the water introduced into gas transfer device 230 may range from lessthan 1 gallon of water per minute to over 200 million gallons of waterper day.

[0107] Based on the above description, the operation of the embodimentof FIG. 8 is now described. Fluid (in this example, water) is pumped viapump 215 from container 205 into inlet tube 220 through first end 221,and the water flows from the first end 221 of inlet tube 220 toward thesecond end 222 of inlet tube 220. Gas (in this example, high purityoxygen) is introduced into the water contained within inlet tube 220 atgas feed 210. In one embodiment, the velocity of the water and highpurity oxygen mixture introduced into gas transfer device 230 throughupper end 232 is approximately 10 feet per second. This high inletvelocity provides turbulence which continually shears the larger bubblesof oxygen gas and maintains a bubble swarm with an exceptionally highgas surface/water volume ratio. Since the bubbles tend to coalesce underlower turbulence which exists at the second portion 233 of gas transferdevice 230, the bubbles are sheared into smaller bubbles at the firstportion 231 of gas transfer device 230 by the vigorous turbulence of thewater and high purity oxygen mixture introduced into gas transfer device230 via inlet tube 220. Thus, the bubble swarm is prevented fromcollapsing and greatly reducing the oxygen absorption rate.

[0108] As the cross section of gas transfer device 230 increases as thewater and oxygen bubble mixture moves toward the second portion 233 ofgas transfer device 230, the downward velocity of the water becomes lessthan the buoyant upward velocity of the bubbles. Therefore, most of thebubbles are retained within gas transfer device 230, while theoxygenated water passes through the first end 241 of outlet tube 240.The oxygenated water flows toward the second end 242 of outlet tube 240and is released outside gas transfer device 230 via second end 242. Asgas transfer device 230 is hydrostatically pressurized due to itsplacement below the fluid surface 207, a high level of oxygen isdissolved into the water, while simultaneously minimizing the problemscaused by stripping the dissolved N₂ from the water into the high purityoxygen phase.

[0109] Instead of hydrostatically pressurizing gas transfer device 230,the pressure can be increased in gas transfer device 230 by pumping thefluid and gas mixture into the gas transfer device against a throttlingvalve of a type well known in the art as the mixture is introduced intogas transfer device 230. However, placing gas transfer device 230 belowfluid surface 207 achieves the necessary pressurization in a much moreenergy efficient manner. If gas transfer device 230 is positioned at thesame level as fluid surface 207, the unit energy consumption forpressurizing gas transfer device 230 for the purpose of dissolvingoxygen is approximately 700 kilowatt-hours per ton of dissolved oxygen.The cost associated with such energy consumption is approximately$220,000. However, the energy consumption decreases to approximately 350kilowatt-hours per ton of dissolved oxygen if midpoint 236 of gastransfer device 230 is positioned 20 feet below fluid surface 207. Thecost associated with such energy consumption is approximately $120,000.The reason for this dramatic decrease in energy consumption is that therequirements for pumping the fluid into gas transfer device 230 do notchange significantly; however, the concentration of dissolved oxygen inthe oxygenated water released from gas transfer device 230 increasesfrom 15 mg/L to 30 mg/L. The concentration of dissolved oxygen in theoxygenated water released from gas transfer device 230 increases as thedepth at which gas transfer device 230 is placed below fluid surface 207increases.

[0110] In one embodiment of the present invention, if midpoint 236 ofgas transfer device 230 is positioned 60 feet below fluid surface 207,the oxygenated water released from the gas transfer device contains aconcentration of 90 mg/L of dissolved oxygen. In the same embodiment ofthe present invention, if midpoint 236 of gas transfer device 230 ispositioned 100 feet below fluid surface 207, the oxygenated waterreleased from gas transfer device 230 contains a concentration of over120 mg/L of dissolved oxygen.

[0111] Water that contains more than air saturated concentrations ofdissolved oxygen is referred to as “superoxygenated” water. However, ifthe discharged water contains over 120 mg/L of dissolved oxygen, some ofthe dissolved oxygen may spontaneously effervesce. Such effervescencecan be minimized, if not eliminated, if second end 242 is positionedwithin container 205 and if the superoxygenated water is released fromsecond end 242 back into container 205, or if the superoxygenated wateris released into some other bulk volume of water that contains lowconcentrations of dissolved oxygen. Further, the low turbulencedepressurization of the oxygenated water as it flows through outlet tube240 also enhances the retention of the dissolved oxygen in thedischarge. In an alternative embodiment of the present invention, theoxygenated water released from second end 242 of outlet tube 240 issubsequently introduced into the apparatuses shown in FIGS. 1, 5, 6, or7 so that additional amounts of oxygen may be dissolved in the waterthrough the operation of these apparatuses as described above.

[0112] It will be appreciated by those of skill in the art thatapparatus 200 may comprise other gas transfer devices besides gastransfer device 230 as long as the gas bubbles are not swept out of thegas transfer device with the water passing through the gas transferdevice, but remain in, or are captured and recycled to the gas transferdevice. In other words, the bubble movement must be uncoupled from thewater movement. This can be accomplished in two ways. The first way isif the vertical downward flow of water through the gas transfer devicecan be reduced to less than the vertical upward buoyant velocity of thegas bubbles, such as through the use of gas transfer device 230. Asecond example of a gas transfer device wherein the vertical downwardflow of water is reduced to less than the vertical upward buoyantvelocity of bubbles is a cylindrical gas transfer device with anaccelerator plate at the top of the gas transfer device which providesthe energy necessary to maintain the bubble swarm so that it does notcollapse. However, at the same time, the downward movement of the waterwithin the cylindrical gas transfer device is less than the buoyantvelocity of the bubbles so that the bubbles are trapped indefinitelywithin the gas transfer device. Such a gas transfer device is the secondembodiment of the present invention shown in FIG.

[0113] The second way to ensure that the bubble movement is uncoupledfrom the water movement is if the bubbles can be harvested from thewater flow through a helix or parallel plate separator or a centrifugalforce, and returned to the gas transfer device. In such gas transferdevices, the downward water velocities are higher than the buoyantvelocity of the bubbles, causing the bubbles to move in the direction ofthe water. However, this bubble and water mixture is then passed througha helix or parallel plate separator or centrifugal force to separate thebubbles and return them to the water flow. An example of this type ofgas transfer device is the fourth embodiment of the present inventionshown in FIG. 7.

[0114] It will be appreciated by those of skill in the art that bypressurizing the gas transfer device shown in FIG. 8, high levels of agas are dissolved into a fluid, and the fluid retains such high levelsof the gas while minimizing the stripping of dissolved N₂ in the fluidintroduced into the gas transfer device. The apparatus does not consumemuch energy as pressurization occurs hydrostatically by the placement ofgas transfer device 230 below fluid surface 207. The embodiment of thepresent invention is particularly useful when a high level of dissolvedoxygen must be achieved in the discharge to match the accumulativeoxygen consumption demand and prevent noxious end products, such as H₂S.Such anaerobic environments include, but are not limited to primaryclarifiers, excessively polluted urban rivers, gravity and force mainsewers, combined sewer overflow storage basins, sludge dewateringoperations, and wastewater lagoons.

[0115] It will also be appreciated that the apparatus of the presentinvention has use in a myriad of other applications. In oxygenation ofwater for example, the present invention may be used for slowly movingrivers and canals, lagoons, reservoirs, fish/shellfish/mussel/shrimpponds, wastewater treatment systems, sewer lift stations, and wastewaterprocessing for various industries; including but not limited to thepharmaceutical, petroleum, food and chemical industries. The presentinvention is also useful for dissolving hydrogen into vegetable oil,hydrogen into coal liquifaction fluids, or for pharmaceutical andindustry aerobic bioprocesses, such as yeast production and Vitamin Cproduction. The present invention also has application for ozonation ofwater or other fluids.

[0116] The foregoing is offered primarily for purposes of illustratingthe apparatus and method of the present invention. It will be readilyapparent to those of skill in the art that the materials, dimensions,operating procedures and conditions, and other parameters of the gasdissolving apparatus and method may be further modified or substantiatedin various ways without departing from the spirit and scope of theinvention.

I claim:
 1. An apparatus for dissolving a gas into a fluid, theapparatus comprising: a container having fluid therein, the fluid havinga surface; a gas transfer device, the gas transfer device having anupper end and a closed bottom end, the gas transfer device positionedbelow the surface of the fluid in the container; a fluid inlet means,the fluid inlet means having a first end for receipt of the fluid fromthe container, and a second end for the introduction of the fluid intothe gas transfer device; a gas inlet means, the gas inlet means operablyconnected to the fluid inlet means between the first end of the fluidinlet means and the second end of the fluid inlet means for introductionof the gas into the fluid before it is introduced into the gas transferdevice; and an outlet means, the outlet means having a first endpositioned within the gas transfer device for receipt of the fluidhaving the gas dissolved therein, and a second end positioned outside ofthe gas transfer device for release of the fluid having the gasdissolved therein from the gas transfer device.
 2. The apparatus ofclaim 1 wherein the fluid comprises water.
 3. The apparatus of claim 1wherein the gas comprises oxygen.
 4. The apparatus of claim 1 whereinthe fluid comprises water and the gas comprises oxygen.
 5. The apparatusof claim 1 wherein the gas transfer device has a generally diverginginside surface.
 6. The apparatus of claim 1 further comprising anacceleration plate positioned within the gas transfer device foracceleration of the fluid and gas mixture therethrough, and wherein thegas transfer device is substantially cylindrical in shape.
 7. Theapparatus of claim 1 further comprising a helix-shaped bubble harvesterpositioned within the gas transfer device.
 8. The apparatus of claim 1wherein the gas transfer device is positioned underground.
 9. Theapparatus of claim 8 wherein the gas transfer device is positioned in anexcavated caisson.
 10. The apparatus of claim 1 wherein the second endof the outlet means is positioned within the container for the releaseof the fluid having the gas dissolved therein into the container. 11.The apparatus of claim 1 wherein a midpoint of a longitudinal axis ofthe gas transfer device is positioned at least about ten feet below thesurface of the fluid in the container.
 12. The apparatus of claim 1further comprising a pumping means operably connected to the first endof the fluid inlet means for pumping the fluid from the container intothe fluid inlet means.
 13. An apparatus for dissolving a gas into fluid,the apparatus comprising: a container having fluid therein, the fluidhaving a surface; a gas transfer device, the gas transfer device havingan upper end and a closed bottom end, the gas transfer device positionedbelow the surface of the fluid in the container; a fluid inlet means,the fluid inlet means having a first end for receipt of the fluid fromthe container, and a second end for the introduction of the fluid intothe gas transfer device; a gas inlet means, the gas inlet means forintroduction of the gas into the gas transfer device; and an outletmeans, the outlet means having a first end positioned within the gastransfer device for receipt of the fluid having the gas dissolvedtherein, and a second end positioned outside of the gas transfer devicefor release of the fluid having the gas dissolved therein from the gastransfer device.
 14. A method for dissolving a gas into a fluid, themethod comprising the steps of: providing a container having the fluidtherein, the fluid having a surface; providing a gas transfer device,the gas transfer device having an upper end and a closed bottom end, thegas transfer device positioned below the surface of fluid in thecontainer; providing a fluid inlet means, the fluid inlet means having afirst end for receipt of the fluid and a second end for the introductionof the fluid into the gas transfer device; providing a gas inlet means,the gas inlet means operably connected to the fluid inlet means betweenthe first end of the fluid inlet means and the second end of the fluidinlet means for introduction of the gas into the fluid before it isintroduced into the gas transfer device; providing an outlet means, theoutlet means having a first end positioned within the gas transferdevice for receipt of the fluid having the gas dissolved therein, and asecond end positioned outside of the gas transfer device for release ofthe fluid having the gas dissolved therein from the gas transfer device;allowing the fluid to flow from the container into the first end of thefluid inlet means; allowing the fluid to flow through the fluid inletmeans; introducing the gas into the fluid through the gas inlet meansbefore it is introduced into the gas transfer device; introducing thefluid and gas mixture into the gas transfer device through the upper endof the gas transfer device via the second end of the fluid inlet means;allowing the fluid and gas mixture to flow downward through the gastransfer device such that bubbles of gas are dissolved into the fluid;allowing the fluid having the gas dissolved therein to enter the firstend of the outlet means and flow toward the second end of the outletmeans; releasing the fluid having the gas dissolved therein from the gastransfer device via the second end of the outlet means; and retainingthe bubbles of gas which are not dissolved into the fluid in the gastransfer device.
 15. The method of claim 14 wherein the fluid compriseswater such that the method results in dissolving the gas into the water.16. The method of claim 14 wherein the gas comprises oxygen such thatthe method results in dissolving the oxygen into the fluid.
 17. Themethod of claim 14 wherein the fluid comprises water and the gascomprises oxygen such that the method results in dissolving the oxygeninto the water.
 18. The method of claim 14 wherein the gas transfer hasa generally diverging inside surface.
 19. The method of claim 14 furthercomprising the steps of: positioning the second end of the outlet meanswithin the container; and releasing the fluid having the gas dissolvedtherein into the container.
 20. The method of claim 14 furthercomprising the step of positioning the gas transfer device underground.21. The method of claim 20 further comprising the step of positioningthe gas transfer device in an excavated caisson.
 22. The method of claim14 further comprising the step of positioning a midpoint of alongitudinal axis of the gas transfer device at least about ten feetbelow the surface of the fluid in the container.
 23. The method of claim14 further comprising the steps of: providing a pumping means operablyconnected to the first end of the fluid inlet means; and pumping thefluid from the container into the first end of the inlet means.
 24. Themethod of dissolving a gas into a fluid, the method comprising the stepsof: providing a container having fluid therein, the fluid having asurface; providing a gas transfer device, the gas transfer device havingan upper end and a closed bottom end, the gas transfer device positionedbelow the surface of the fluid in the container, the gas transfer devicebeing substantially cylindrical in shape; providing a fluid inlet means,the fluid inlet means having a first end for receipt of the fluid and asecond end for the introduction of the fluid into the gas transferdevice; providing a gas inlet means, the gas inlet means operablyconnected to the fluid inlet means between the first end of the fluidinlet means and the second end of the fluid inlet means for introductionof the gas into the fluid before it is introduced into the gas transferdevice; providing an acceleration plate positioned within the gastransfer device for acceleration of the fluid and gas mixturetherethrough; providing an outlet means, the outlet means having a firstend positioned within the gas transfer device for receipt of the fluidhaving the gas dissolved therein, and a second end positioned outside ofthe gas transfer device for release of the fluid having the gasdissolved therein from the gas transfer device; allowing the fluid toflow from the container to the first end of the fluid inlet means;allowing the fluid to flow through the fluid inlet means; introducingthe gas into the fluid through the gas inlet means before it isintroduced into the gas transfer device; introducing the fluid and gasmixture into the gas transfer device through the upper end of the gastransfer device via the second end of the fluid inlet means; allowingthe fluid and gas mixture to flow downward through the accelerationmeans and the gas transfer device such that bubbles of gas are dissolvedinto the fluid; allowing the fluid having the gas dissolved therein toenter the first end of the outlet means and flow toward the second endof the outlet means; releasing the fluid having the gas dissolved intothe fluid therein from the gas transfer device via the second end of theoutlet means; and retaining the bubbles of gas which are not dissolvedinto the fluid in the gas transfer device.
 25. A method of dissolving agas into a fluid, the method comprising the steps of: providing acontainer having fluid therein, the fluid having a surface; providing agas transfer device, the gas transfer device having an upper end and aclosed bottom end, the gas transfer device positioned below the surfaceof the fluid in the container; providing a fluid inlet means, the fluidinlet means having a first end for receipt of the fluid and a second endfor the introduction of the fluid into the gas transfer device;providing a gas inlet means, the gas inlet means operably connected tothe fluid inlet means between the first end of the fluid inlet means andthe second end of the fluid inlet means for introduction of the gas intothe fluid before it is introduced into the gas transfer device;providing a helix-shaped bubble harvester positioned within the gastransfer device; providing an outlet means, the outlet means having afirst end positioned within the gas transfer device for receipt of thefluid having the gas dissolved therein, and a second end positionedoutside of the gas transfer device for release of fluid having the gasdissolved therein from the gas transfer device; allowing the fluid toflow from the container into the first end of the fluid inlet means;allowing the fluid to flow through the fluid inlet means; introducingthe gas into the fluid through the gas inlet means before it isintroduced into the gas transfer device; introducing the fluid and gasmixture into the gas transfer device through the upper end of the gastransfer device via the fluid inlet means; allowing the fluid and gasmixture to flow downward through the gas transfer device such thatbubbles of gas travel downward to the helix-shaped bubble harvesterwhere the bubbles are kept in contact with the fluid for dissolving atleast a portion of the gas into the fluid; allowing the fluid having thegas dissolved therein to enter the first end of the outlet means andflow toward the second end of the outlet means; releasing the fluidhaving the gas dissolved therein from the gas transfer device via thesecond end of the outlet means; and retaining the bubbles of gas whichare not dissolved into the fluid in the gas transfer device.
 26. Amethod for dissolving a gas into a fluid, the apparatus comprising:providing a container having fluid therein, the fluid having a surface;providing a gas transfer device, the gas transfer device having an upperend and a closed bottom end, the gas transfer device positioned belowthe surface of the fluid in the container; providing a fluid inletmeans, the fluid inlet means having a first end for receipt of the fluidfrom the container, and a second end for the introduction of the fluidinto the gas transfer device; providing a gas inlet means, the gas inletmeans for introduction of the gas into the gas transfer device;providing an outlet means, the outlet means having a first endpositioned within the gas transfer device for receipt of the fluidhaving the gas dissolved therein, and a second end positioned outside ofthe gas transfer device for release of the fluid having the gasdissolved therein from the gas transfer device; allowing the fluid toflow from the container into the first end of the fluid inlet means;allowing the fluid to flow through the fluid inlet means; introducingthe fluid into the gas transfer device via the second end of the fluidinlet means; introducing the gas into the gas transfer device via thegas inlet means; allowing the fluid and gas mixture to flow downwardthrough the gas transfer device such that bubbles of gas are dissolvedinto the fluid; allowing the fluid having the gas dissolved therein toenter the first end of the outlet means and flow toward the second endof the outlet means; releasing the fluid having the gas dissolvedtherein from the gas transfer device via the second end of the outletmeans; and retaining the bubbles of gas which are not dissolved into thefluid in the gas transfer device.